Ultra-local model–based fixed-time adaptive robust sliding mode control of overhead cranes suffering from matched and mismatched disturbances

In order to minimize the impact of control performance by complex external disturbances, convergence of the control trolley and cable length to the desired position at a fixed time is accompanied by complete elimination of the load swing angle. A composite disturbance observer–based sliding mode control strategy for overhead cranes is investigated and proposed. Initially, a nonlinear adaptive sliding mode surface is proposed to accelerate the driving system state variables to the desired positions, and the adaptive sliding mode surface has a fixed-time property without depending on the initial state of the system. Moreover, a composite disturbance observer is proposed to solve the problem that the sliding mode control is difficult to deal with mismatched disturbances. Then, an improved ultra-local model that considers composite disturbances is proposed to reduce the dependence on the exact model of the controlled object. Finally, the stability of the entire control scheme and the convergence of the state variables are proved using Lyapunov stability theory, and the feasibility and advantages of the control strategy are verified by numerical simulations.